Receiver of telephonic or telegraphic signals



Aug 193-. R. PROCHNOW I RECEIVER OF TELEPHONIG OR TELEGRAPHIC SIGNALS 2 sheets-sheet 2 Filed May 28, 1957 4. E AMPLIFIER use/1mm F I INVENTOR f? U 00 L F PROCHNOW BY 7%? TORNEY Patent ed Aug. 9, 1938 UNITED STATES 2,125,953 RECEIVER or TELEPHONIG on TELE- GRAPHIC SIGNALS Rudolf Prochnow, Berlin, Germany, assignor to Telefunken Gesellschaft fur Drahtlose Telegraphic in. b. IL, Berlin, Germany, a corpora tion of Germany Application May 28, 1937, Serial No. 145,196

In Germany March 16, 1936 4 Claims.

The general aim to simplify the operation of commercial receiver apparatus involves the problem to make the change from reception of telegraphic signals to telephonic signal reception automatic. It has been suggested in the prior art to utilize for the said change the direct current component resulting from the rectification of the incoming radio frequency signals by feeding the direct current voltage produced by the carrier wave to a time-lag relay which responds only to impulses of long duration. Inasmuch as in telegraphic work the direct current component varies at the rhythm and rate of the signals between, zero and maximum, whereas it is constant in the reception of telephonic signals the relay responds only to telephone signal reception, and disconnects the heterodyne employed in the reception of telegraphic signals.

However, this method involves a number of troublesome disadvantages. The change, as will be noted, is a function of the telegraphing speed. If the signals are of long duration it may happen that the automatic device disconnects the heterodyne although no modulated signals (telephony) are present. This is due to the fact that the time-lag of the relay cannot be pushed to any desired limit. Moreover, in. the case of transmitters comprising means insuring automatic blocking of the carrier between words (quiescent aerial radiation) the time lapses of telephonic signals are liable to have only the length of a somewhat long telegraphic signal. It will be seen therefrom that the change is apt to be attended with inaccuracies and defects in systems of the said sort.

In order to obviate the said defects, a receiver for selective reception of telephonic and nonmusical telegraphic signals, according to this invention, is so designed that automatic change in connections is accomplished by the aid of rectified telephony modulation.

In describing my invention more in detail reference will be made to Figures 1 to 3 of the draw" ings, each of which show a different embodiment of my receiver with the control means which puts the continuous wave oscillator in or out of operation, depending on the type of signal received.

This scheme insures another advantage in that, under certain circumstances, a distinct relay may be dispensed with if the heterodyne is caused to break off directly by the rectified audio frequency voltage, as shall be shown in more detail further below by reference to Fig. 2. There results the further advantage that also musical telegraphy signals may be picked up without a heterodyne so that there results a clean note.

Modulation must be derived from the receiver, of course, at a point where the heterodyne frequency required for the reception of telegraphic signa1$ has not yet been added. This will be feasible only if reception of telegraphic signals is effected by sonic (audio frequency) modulation of the first heterodyne of a superheterodyne receiver apparatus. However, it is possible in this case to filter this note so that the change mechanism will not respondto the said modulation frequency.v

, Now, the invention shall be explained in more detail by reference to the accompanying drawings which show the radio frequency amplifier first detector and initial intermediate frequency amplifiers, of a heterodyne receiver diagrammatically, that is, by rectangles and then shows the elements starting from the second intermediate frequency amplifier tube in detail.

In the plate circuit of the intermediate frequency amplifier tube H] of Fig. 1 is included a circuit I tuned to the intermediate frequency, and furthermore, an audio frequency coupler transformer 2. If the grid biasing voltage for IE! is properly chosen, this stage acts as a radio frequency amplifier and a rectifier. In coupling relation' with the tuning circuit l is the second heterodyne oscillator tube 20 which is fed with plate potential by way of the resting contact 22 of magnet relay 3. Mixing of the incoming wave, 1. e., the intermediate frequency output of III, and the auxiliary wave supplied by 20, is effected in the rectifier circuit 4. The heterodyne voltage transformed in. the circuit is so chosen that it will not contribute any appreciable amount to thevolume control potential. The regulation voltage, on the contrary, is a function of the amplitude of the receiver input potential. Such telegraphic signals as may be received produce, when beat with oscillations from the second heterodyne 2i), beat notes which are fed by way of the audio frequency amplifier 30 to the headphones. Across the output terminals of the audio frequency coupler 2, on the other hand, an alternating voltage will exist only in case of telephonic reception. This voltage is then amplified by audio frequency amplifier i0, is then rectified by full-wave rectifier 50 and then fed to the relay 3. It will be clear that the second heterodyne 20 can be disconnected by the relay only in case of telephony signals. The receiver is always ready to receive telegraphic signals, and it is changed over in case modulated signals are coming in.

According to another object of the invention, the relay is to be dispensed with as shown in Fig. 2. In this arrangement the alternating potential furnished from the audio frequency amplifier is rectified and is used as a counter-voltage for a glow tube 8. The output of 50 supplies voltage to a resistor 6!] in the direct current circuit of 8. The resistor 60 is poled to oppose the potential supplied by the direct current circuit to 8. The glow tube circuit is a voltage divider for the screen grid potential of the second heterodyne 20 and supplies the plate potential also. When the audio frequency voltage supplied by 2, 40 and has attained a certain value in the presence ofsmall or no telephony modulations on the received" wave, the said glow tube is caused to go out, and

amplifier stage 40 in a reflex circuit scheme may be combined with the preceding stages of the receiver equipment. make sure that this tube will not be afiected by the automatic volume control regulation, other wise it will not operate to cause the receiver to respond to telegraphy except in the presence of telephony.

Another circuit organization is shown in Fig. 3. Inthis scheme the voltage arising across the coupler 2 in the presence of telephonic signals is rectified and is used in the form of a negative grid bias for the power tube 30 of the audio frequency amplifier; The plate circuit of the said power tube moreover contains, in addition to the output coupler 6, also a relay 3 which responds to'a change of the plate current of about 2 milliamps. In case of telegraphy signals, the power tube 30 operates only with a very low negative biasing voltage. This is readily possible since distortions are immaterial. In the presence of modulated signals the powertube will be more strongly biased so that the incidentally caused change in the plate current disconnects the plate circuit of the second heterodyne 20 bythe action of relay 3.

In conclusion, certain phenomena shall be discussed which are liable to endanger satisfactory operation of the scheme. Roaring noises, which are likely to arise in receivers of high sensitiveness and which, so far as their action is concerned, are similar to the modulation of a signal may cause the automatic mechanism to respond unless precautionary steps are taken. It is suggested to tune the audio frequency coupler 2 to around 1000 cycles with the consequence that the high frequencies are suppressed.

The incoming signals, moreover, must have a certain amplitude in order that the automatic device may be operated. It will be readily understood that unduly feeble signals will lead to failure of the automatic device so much less frequently, the steeper the regulation characteristic of the volume control means.

I claim:

1. In a receiving system to be used for the reception of telegraphy or telephony signals, a wave amplifier and rectifier, means for impressing said signals on said amplifier, a utilization circuit responsive to wave energy coupled to the output of said rectifier, a local oscillator coupled to said wave amplifier and rectifier and normally'operative to impress beating oscillations thereon when continuous wave energy is impressed on said amplifier, the resulting beat note being impressed on said utilization circuit, and additional means coupled to' said' rectifier and associated with said oscillator for rendering said oscillator inoperative when signal modulated waves are impressed on said'wave amplifying means.

2. In a system for the reception of Wave energy modulated by telephony signals or by nonmus ic'al telegraphy signals, wave receiving amplifying and demodulating means of the heterodyne type having an'input on which the wave energy is impressedand an output from which intermediate All that is'necessary is to frequency energy is derived, a'rectifier having an input coupled to said output, said rectifier having an. output, an amplifier circuit having input electrodes and having output electrodes coupled to a "utilization circuit, a second rectifier coupling the input of said amplifier to the output of said first rectifier, a local oscillator coupled to said first rectifier to impress thereon oscillations to be beat with the intermediate frequency wave energy when the received wave is modulated by nonmusical telegraphy signals, said oscillator being normally operative, and additional rectifying means excited by energy from the output of said first rectifier for rendering said oscillator inoperative when said received wave energy is modulated by telephony signals. r

3. In a system for receiving wave energy modulated by telephony signals or by non-musical telegraphy signals, a demodulator of the heterodyne type'including a source of' oscillations anda first detector excited by received wave energy and by oscillations from said source of oscillators, means for deriving from said detector the beat frequency produced by beating said received wave energy with said oscillations, a beat frequency amplifier tube having input and output electrodes, means for impressing said beat frequency on said input electrodes, means for biasing the electrodes of said tube to produce plate rectification in said tube, an output circuit connected with said output electrodes, a utilization circuit coupled by a rectifier to said output circuit, an additional rectifier of the full wave type having input electrodes coupled to said output circuit and having output electrodes connected in a relay circuit, an additional oscillator coupled to said output circuit to supply oscillations thereto, and means connecting said relay with a circuit of said additional oscillator to render'the same inoperative when said received wave energy is modulated by telephony signals.

4. In a system for receiving wave energy modulated by telephony signals or by non-musical telegraphy signals, a local oscillator, a first detector, means for impressing oscillations from said oscillator on said first detector and wave energy to be demodulated on said first detector, an output circuit coupled with said first detector, said output circuit being responsive to the beat frequency between said wave energy and said oscillations from said local oscillator, a beat frequency amplifier and rectifier of the electron dischargetube type having a control grid coupled with said output circuit and having an anode connected in an alternating current output circuit, means for biasing the electrodes of said discharge tube to produce plate rectification therein, a utilization circuit, an electron discharge tube amplifier having an anode coupled to said utilization circuit and having a control electrode, a rectifier coupling said controlling electrode to said second named output circuit, means in said second named output circuit responsive only to current components resulting from the rectification of wave energy modulated by telephony signals in said amplifier and rectifier, a third rectifier coupling said last named circuit to the control electrode of said electron discharge tube amplifier, a local oscillator coupled to said second named output circuit, and a relay coupling the anode of said electrondischarge tube amplifier to a circuit of said local oscillator to control the operativeness thereof.

RUDOLF PROCHNOW. 

